\nSo, let’s start Spring\u00a0Dependency Injection.<\/p>\n
![\"Spring](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2018\/07\/Spring-Dependency-Injection-01.jpg\")
<\/a>Spring Dependency Injection – Types of Spring DI & Example<\/p><\/div>\n
2. What is Spring Dependency Injection?<\/h2>\n
As you know every Java-based applications have few objects that work as one so as to present it like a working application. While writing a very complex Java-based application, the classes of it should be made as independent as possible of the other Java classes<\/strong><\/a>. So, as to increase the possibility of reuse of it. Also, with that, you can test them separately while performing unit testing. Wiring or commonly known as Spring Dependency Injection<\/em> guides in sticking these classes together while keeping them independent. So, the thing that is done in the code above is a creation of a dependency between a TextEditor and the SpellCheker. While doing IoC Container<\/strong> <\/a>you should do something like:<\/p>\n The TextEditor here shouldn\u2019t worry about the implementation of the SpellChecker. Instead, the SpellChecker should be implemented separately and should be provided to the TextEditor while doing the instantiation of the TextEditor. This process is entirely controlled by the Spring Framework. The two major types of Spring Framework Dependency Injection are:<\/p>\n The Constructor-based Spring Dependency Injection is attained when the class constructor is invoked by the container with the number of arguments each having a dependency on other class. Here is TextEditor.java file code:<\/strong> Following is the code for SpellChecker.java:<\/strong> The MainApp.java is defined as:<\/strong> The Bean.xml Config file is defined as:<\/strong><\/p>\n Once you have created the files run the application for the result. If everything is working fine the following output message is achieved: The Setter Based Spring Dependency Injection, is attained by calling the setter methods on the beans after invoking no-arg constructor using the Bean container. Here is TextEditor.java file code:<\/strong> The code for SpellChecker.java is:<\/strong> Following is the code for MainApp.java:<\/strong> Follow this link to know about Spring Boot CLI\u00a0<\/a><\/strong> Once you have created the files run the application for the result. If everything is working fine the following output message is achieved: Hence, in this Spring DI Tutorial, we studied the Spring Dependency Injection. Along with that, we discussed the types of Dependency Injections in Spring Framework. Also, working examples of both the types of Spring dependency injection was explained with the help of working example using Eclipse IDE. Furthermore, if you have any query, feel free to ask in the comment box. 1. Objective In our last tutorial, we studied Spring Web Services. Today in this Spring tutorial, we will learn about one of the important topics of Spring Framework which is Spring Dependency Injection. Along...<\/p>\n","protected":false},"author":5,"featured_media":20501,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[64],"tags":[2936,3759,4354,7165,12784,13290],"class_list":["post-20485","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-spring","tag-constructor-based-di","tag-dependency-injection-java","tag-example-of-spring-dependency-injection","tag-inversion-of-control-in-spring","tag-setter-based-di","tag-spring-dependency-injection"],"yoast_head":"\n
\nDo you know the Advantages of Spring Framework<\/a><\/strong>
\nConsider an application having text editor component in which you want to add a spell checker. You try to code like:<\/p>\npublic class TextEditor {\r\n\u00a0\u00a0 private SpellChecker spellChecker;\r\n\u00a0\u00a0 public TextEditor() {\r\n\u00a0\u00a0\u00a0 \u00a0\u00a0spellChecker = new SpellChecker();\r\n\u00a0\u00a0 }\r\n}<\/pre>\npublic class TextEditor {\r\n\u00a0\u00a0 private SpellChecker spellChecker;\r\n\u00a0\u00a0\u00a0\u00a0 public TextEditor(SpellChecker spellChecker) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 this.spellChecker = spellChecker;\r\n\u00a0\u00a0 }\r\n}<\/pre>\n
\nNow after removing the entire control from the TextEditor and then keeping it somewhere else and the Dependency that is SpellChecker is injected into the TextEditor class via a Class Constructor. Therefore, the flow of control is being inverted by the Spring Dependency Injection as you have delegated the dependencies to some external system.
\nAnother method of injecting the dependency is via Setter methods of the class TextEditor where the SpellChecker instantiation is created. This will be used for calling the setter methods to initialize the TextEditor properties.
\nRead about Spring Bean Definition \u2013 Spring Configuration Metadata<\/a><\/strong><\/p>\n3. Types of Dependency Injection in Spring Framework<\/h2>\n
a. Constructor-Based Dependency Injection<\/h3>\n
\nThe following is a working example having a class TextEditor in which dependency is injected using constructor injection:<\/p>\n\n
\npackage com.example;<\/strong><\/p>\npublic class TextEditor {\r\n\u00a0\u00a0 private SpellChecker spellChecker;\r\n\u00a0\u00a0 public TextEditor(SpellChecker spellChecker) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside TextEditor constructor.\" );\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 this.spellChecker = spellChecker;\r\n\u00a0\u00a0 }\r\n\u00a0 public void spellCheck() {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 spellChecker.checkSpelling();\r\n\u00a0 }\r\n}<\/pre>\n
\npackage com.example;<\/strong><\/p>\npublic class SpellChecker {\r\n\u00a0\u00a0 public SpellChecker(){\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside SpellChecker constructor.\" );\r\n\u00a0\u00a0 }\r\n\u00a0\u00a0 public void checkSpelling() {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside checkSpelling.\" );\r\n\u00a0\u00a0 }\r\n}<\/pre>\n
\npackage com.example;<\/strong><\/p>\nimport org.springframework.context.ApplicationContext;\r\nimport org.springframework.context.support.ClassPathXmlApplicationContext;\r\npublic class MainApp {\r\n\u00a0\u00a0 public static void main(String[] args) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 ApplicationContext context = new ClassPathXmlApplicationContext(\"Beans.xml\");\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 TextEditor te = (TextEditor) context.getBean(\"textEditor\");\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 te.spellCheck();\r\n\u00a0\u00a0 }\r\n}<\/pre>\n<?xml version = \"1.0\" encoding = \"UTF-8\"?>\r\n<beans xmlns = \"http:\/\/www.springframework.org\/schema\/beans\"\r\n\u00a0\u00a0 xmlns:xsi = \"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\r\n\u00a0\u00a0 xsi:schemaLocation = \"http:\/\/www.springframework.org\/schema\/beans\r\n\u00a0\u00a0 http:\/\/www.springframework.org\/schema\/beans\/spring-beans-3.0.xsd\">\r\n\u00a0\u00a0 <!-- Definition for textEditor bean -->\r\n\u00a0\u00a0 <bean id = \"textEditor\" class = \"com.example.TextEditor\">\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 <constructor-arg ref = \"spellChecker\"\/>\r\n\u00a0\u00a0 <\/bean>\r\n\u00a0\u00a0 <!-- Definition for spellChecker bean -->\r\n\u00a0\u00a0 <bean id = \"spellChecker\" class = \"com.example.SpellChecker\"><\/bean>\r\n<\/beans><\/pre>\n
\nOutput –<\/strong>Inside SpellChecker constructor.
\nInside TextEditor constructor.
\nInside checkSpelling.
\nHave a Look Integration of MVC with Spring<\/a><\/strong><\/p>\nb. Setter Based Dependency Injection<\/h3>\n
\nThe following is a working example having a class TextEditor in which dependency is injected using constructor injection:<\/p>\n\n
\npackage com.example;<\/strong><\/p>\npublic class TextEditor {\r\n\u00a0\u00a0 private SpellChecker spellChecker;\r\n\u00a0\u00a0 \/\/ a setter method to inject the dependency.\r\n\u00a0\u00a0 public void setSpellChecker(SpellChecker spellChecker) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside setSpellChecker.\" );\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 this.spellChecker = spellChecker;\r\n\u00a0\u00a0 }\r\n\u00a0\u00a0 \/\/ a getter method to return spellChecker\r\n\u00a0\u00a0 public SpellChecker getSpellChecker() {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 return spellChecker;\r\n\u00a0 }\r\n\u00a0\u00a0 public void spellCheck() {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 spellChecker.checkSpelling();\r\n\u00a0\u00a0 }\r\n}<\/pre>\n
\npackage com.example;<\/strong><\/p>\npublic class SpellChecker {\r\n\u00a0\u00a0 public SpellChecker(){\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside SpellChecker constructor.\" );\r\n\u00a0\u00a0 }\r\n\u00a0\u00a0 public void checkSpelling() {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(\"Inside checkSpelling.\" );\r\n }\r\n}<\/pre>\n
\npackage com.example;<\/strong><\/p>\nimport org.springframework.context.ApplicationContext;\r\nimport org.springframework.context.support.ClassPathXmlApplicationContext;\r\npublic class MainApp {\r\n\u00a0 public static void main(String[] args) {\r\n\u00a0\u00a0\u00a0\u00a0 \u00a0ApplicationContext context = new ClassPathXmlApplicationContext(\"Beans.xml\");\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 TextEditor te = (TextEditor) context.getBean(\"textEditor\");\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 te.spellCheck();\r\n\u00a0\u00a0 }\r\n}<\/pre>\n
\nThe config file Beans.xml is defined as:<\/strong><\/p>\n<?xml version = \"1.0\" encoding = \"UTF-8\"?>\r\n<beans xmlns = \"http:\/\/www.springframework.org\/schema\/beans\"\r\n\u00a0\u00a0 xmlns:xsi = \"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\r\n\u00a0\u00a0 xsi:schemaLocation = \"http:\/\/www.springframework.org\/schema\/beans\r\n\u00a0\u00a0 http:\/\/www.springframework.org\/schema\/beans\/spring-beans-3.0.xsd\">\r\n\u00a0\u00a0 <!-- Definition for textEditor bean -->\r\n\u00a0\u00a0 <bean id = \"textEditor\" class = \"com.example.TextEditor\">\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 <property name = \"spellChecker\" ref = \"spellChecker\"\/>\r\n\u00a0\u00a0 <\/bean>\r\n\u00a0\u00a0 <!-- Definition for spellChecker bean -->\r\n\u00a0\u00a0 <bean id = \"spellChecker\" class = \"com.example.SpellChecker\"><\/bean>\r\n<\/beans><\/pre>\n
\nOutput – <\/strong>Inside SpellChecker constructor.
\nInside TextEditor constructor.
\nInside checkSpelling.
\nSo, this was all about Spring\u00a0Dependency Injection. Hope you like our explanation.<\/p>\n4. Conclusion<\/h2>\n
\nRelated Topic-\u00a0Spring Bean Life Cycle<\/a><\/strong>
\nFor reference<\/a><\/strong><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"